Ever stricter legal requirements in terms of admissible emissions of pollutants of motor vehicles in which internal combustion engines are arranged make it necessary to keep the emissions of pollutants as low as possible during operation of the internal combustion engine. This can occur, on the one hand, by virtue of the fact that there is a reduction in the emissions of pollutants which are produced during the combustion of the air/fuel mixture in the respective cylinder of the internal combustion engine. On the other hand, exhaust gas post-treatment systems are in use in internal combustion engines, which exhaust gas post-treatment systems convert the emissions of pollutants which are generated during the combustion process of the air/fuel mixture in the respective cylinders into harmless substances. For this purpose, exhaust gas catalytic converters are used which convert carbon monoxide, hydrocarbons and nitrogen oxides into harmless substances. Both the targeted influencing of the generation of the emissions of pollutants during the combustion and the conversion of the components of the pollutants with a high level of efficiency by the exhaust gas catalytic converter require a very precisely set air/fuel ratio in the respective cylinder.
Furthermore, ever stricter requirements are also with respect to the diagnosis of components which are relevant to pollutants. For example, dynamically slow exhaust gas probes have an adverse effect on the emissions of pollutants. In this respect, the detection of dynamically slow exhaust gas probes is an important element for meeting legal requirements, such as the on-board diagnostic regulations (OBD). Previously, the regulations for on-board diagnostics concentrated on symmetrically aged probes, that is to say the dynamics of the rich/lean and lean/rich direction did not differ significantly. More recent OBD regulations now also require asymmetrically aged exhaust gas probes to be detected. Here, it is assumed that the impairment of the dynamics acts in only one direction, while the other direction still has a nominal behavior. Along with an asymmetrically aged exhaust gas probe there is significant worsening of the emissions of pollutants owing to displacement of the center position of the mixture. This is based on differences between the measured profile and the expected profile of the excess air ratio during the forced excitation. The lambda control reacts to this and displaces the center position of the mixture in accordance with the asymmetry.